The 9mm x 18 mm Makarov was probably developed in 1947-1948.
The earliest known headstamp is dated 1949 (711 * 49 *).

Datig speculates that the round was derived, or at least
heavily inspired, by Fritz Walter’s 9mm Ultra design in that it utilized a
straight case (and thus allowing for a pistol design that used an unlocked
breech and blowback operation). If you kept the 9mm Parabellum bullet and case
mouth dimensions and made a straight-sided case by reducing the diameter of the
base, then you’d be approaching the 9mm Ultra. Conversely, if you took the 9mm
Parabellum case and made a straight sided case from the base up (and shortened
it by 1mm), then you’d have a 9mm Makarov. The Makarov projectile is 9.25mm in diameter
(and necessarily slightly larger than the 9mm Parabellum).

Alternatively, the cartridge may have been developed from
scratch as the design of the weapon called for a blow-back design for which the
straight case is better suited.

Regardless, until the fall of communism, the ammunition and
weapons were produced in the Soviet Union (USSR), East Germany (DDR), China (PRC) and Bulgaria. Poland, Hungary and
Czechoslovakia also made ammunition. Note that both Hungary and Poland both use
factory code ‘21' but the Polish headstamp date is upside down.

An interesting observation is that for Russian (Soviet)
produced brass cased ammunition was only loaded with lead cored ammunition
while steel cased ammunition used the steel and lead core.